In this work, we present ab initio calculations of structural and electronic properties of Ta impurities, located in a substitutional cation site of the SnO2 semiconductor. The calculation were performed using the Full Potential Augmented Plane Wave plus local orbitals (FP-APW+lo) method, in the framework of the Density Functional Theory, with the implementation of the WIEN2k code. The calculations of the Electric Field Gradient tensor (EFG) are compared with experimental results come from the Time Differential Perturbed Angular Correlations technique, where the impurity dilution in ppm. In order to obtain in the ab initio calculations an impurity dilution where the impurity and its neighbors don´t sense the effects produced by the probe and its neighbors, and to reproduce correctly de experimental results, we use supercells. Since the Ta impurity is a single donor in SnO2 when it replaces a Sn atom, we performed calculations for two charge states: neutral (replacing a Sn atom by a Ta one in the supercell) and charged (removing one electron in the supercell). Although Ta produces contractions in the host of SnO2, contrarily to happen in TiO2 [1] (isomorphs to SnO2 where produces dilatations), the final positions between the impurity and its nearest neighbors try to reconstruct the distance of Ta-O in Ta2O5. Finally, the results are comnpared with those obtained with Cd impurity in SnO2 (which have diferent electronic structure tan Ta). [1] G. N. Darriba, L. A. Errico, P. D. Eversheim, G. Fabricius, and M. Renter´ıa, Phys. Rev. B 79, 115213 (2009).